There are many potential applications for single-crystal silicon films grown over insulators (SOI). The potential exists for producing vertically integrated, three-dimensional circuits having greatly increased packing densities and for dielectric isolation of MOS devices for improved performance, as in high-voltage switching devices of MOS circuits in which the p-channel transistor would be placed in the SOI film and completely isolated from the n-channel transistor with trench oxide to eliminate "latch-up" between devices. In response to these goals, different SOI processes, such as laser-beam, electron-beam and strip-heater recrystallization, have been developed. An alternative is the lateral growth of silicon over oxide stripes on a silicon wafer during chemical vapor deposition of the silicon layer.
A similar substrate can be used in all of these processes. This substrate consists of, for example, a &lt;100&gt; silicon wafer covered with silicon dioxide which is then etched by standard photolithographic techniques to form oxide stripes in the &lt;100&gt; direction with silicon seed areas adjacent to the oxide stripes. In the laser-beam, electron-beam, and strip-heater methods a uniform film of polysilicon is deposited over the oxide-striped substrate; then the deposited polysilicon is melted by scanning the surface with a beam or with a hot wire (strip-heater approach). As the molten silicon over the seed area solidifies, its crystal structure continues that of the substrate. Ideally, this same structure also continues into the silicon film over the oxide surface as the silicon solidifies.